In the manufacturing of electronic devices used in microelectronic applications, a lead frame is often employed between the molded base and lid components of a chip package. The lead frame is typically a metal or a metal alloy of about 0.01 inch thick and is connected to the output terminals of the chip with a plurality of tiny bond wires.
Recently, there has been an increased tendency for electronic device manufacturers to increase circuit density. As this circuitry becomes more densified, a larger number of terminal paths and leads are required to contact the chip with the printed circuit board. Conventional lead frames are suitable for devices requiring about 16 to 32 leads. However, since modern chips may require many times this traditional number of leads, conventional lead frames, and the leads extending from these lead frames, are not considered satisfactory.
Prior artisans have attempted to increase the lead count through better alignment of the lead frame and the use of thinner lead frames, also called tape lead frames, which provide thinner stock material for permitting closer spacing between leads. Although these lead assemblies permit closer spacing, flexibility, mechanical strength, and registration are often a problem. Metal tape also has little structural strength on its own and is difficult to position properly.
Although automated bonding and photolithography have minimized some of the deficiencies associated with thin leads, device density continues to outrun the permissible number of leads dictated by current technology.